There is a method in which whether or not a specific detection object which is desired to be detected is present in a picked-up image is determined using a previously formed classifier. How the detection object present in the image looks changes variously according to a minute difference in viewing direction or a minute difference between individual objects. Even when there are such differences, in order to keep the detection precision, the feature vectors are calculated from the image, so that the object is discriminated based on the feature vectors.
When the detection object has a specific color, there is a method using the color. However, the color largely varies depending upon imaging environment such as the color of illumination and setting of a camera. Thus, when the color in a specific region in the picked-up image is known, there is proposed a method in which a detection object is detected using the relative color relationship with the color. For example, in JP-A-2007-122218 (U.S. Patent Application Publication No. 2007/0092134), in order to detect a hand, a face, which is relatively easy to detect, is firstly detected. Then, hand detection is performed in the candidate image region of the hand which has a color close to the skin color of the detected face. However, with this method, when an object similar in color to the face is present in the image, the hand region is not extracted properly. Accordingly, the position and the shape cannot be determined properly.
In TEMPLATE-BASED HAND POSE RECOGNITION USING MULTIPLE CUES, B. Stenger, Proc. ACCV, pages 551-560, January 2006, similarly, a face is detected to form a skin color model. Using the gradient direction of the skin color intensity calculated using the skin color model, a hand is detected by temperate matching. However template matching is not robust against changes in shape of the hand.